The manufacture and various uses of polyolefin-based fibers and corresponding nonwoven materials are well known in the textile art. Attempts to apply such knowledge to produce products in the area of personal hygiene, such as cover stocks for catamenial devices, disposable diapers, and incontinence pads, have met with limited success. Such products must have a fluid-absorbent core, usually comprising one or more layers of fluid absorbent material such as wood pulp, gauze, or tissue and, in some cases, synthetic hydrophilic material, such as hydrophilic polyurethane foam.
The fluid-absorbing material is typically provided in the form of a thermally bonded pad. To protect the clothing or areas around the user from being stained or wetted by fluids absorbed by the pad, the pad may be backed by a fluid impervious barrier sheet. The absorbent product is typically positioned against the body with the hydrophilic material facing and contacting the body and the fluid impervious barrier layer facing the outside. To enhance a sense of comfort, such absorbent products also generally employ a facing or cover stock material which covers the body-facing surface of the product. The facing or cover stock must be very pervious to fluids on the side of the product that is placed against the body, and yet be essentially nonabsorbent. Such material should also feel smooth and soft to the touch. In addition, certain additional characteristics are also sometimes desire, such as visual opacity, specific coloring, and luster on the outer surfaces.
In order to obtain many of above-listed characteristics, a cover stock utilizing essentially hydrophobic polymeric material, such as polyolefin fiber or film, may be made at least temporarily hydrophilic yet have the continuing ability to pass aqueous fluids through. This is particularly important in the case of diaper cover stock so as to avoid lateral liquid migration and side leakage without interfering with fabric bonding steps or wet strength of the final product.
Based on the teaching in the paper-making art, it is known that short term hydrophilicity can be imparted to hydrophobic polymers such as polyolefin fiber by using flash evaporation techniques and treating the resulting fiber or filament with hydrophilizing agents such as polyvinyl alcohol or various nitrogen-containing water-soluble polymers. Efforts to incorporate an alkoxylated alkylphenols or corresponding polyoxyalkylenes into spun melt fiber compositions are disclosed in U.S. Pat. No. 4,578,414.
U.S. Pat. No. 5,033,172 discloses that the hydrophilicity and liquid strike through properties of fiber can be retained for an extended period by incorporating into the polyolefin composition an effective amount of a modifier composition. In U.S. Pat. No. 4,853,290, a blend of ethylene-acrylic acid copolymer and ethylene-methylacrylate copolymer is coextruded onto a polypropylene film. U.S. Pat. Nos. 3,373,222 and 3,373,223 disclose polymeric blends comprising a polyolefin resin, a polyamide resin, and either a carboxylated polyethylene, an ethylene-acrylic or a methacrylic acid copolymer. U.S. Pat. No. 5,033,172 discloses a hydrophobic polyolefin containing nonwoven material which may contain up to 60% by weight of a particular modifier composition.
U.S. Pat. Nos. 4,540,414 and 4,550,725 disclose a nonwoven polypropylene fabric designed for removal of moisture from the skin of a human being covered by the fabric. U.S. Pat. Nos. 4,372,310, 4,892,532 and 4,892,534 disclose particular arrangements of liquid absorbing fabrics and fabric layers suitable for forming a diaper material. U.S. Pat. No. 4,804,378 discloses a material suitable for forming a sheet having a hydrophilic surface and a hydrophobic inside. European Patent Publication Nos. 0307116 and 0192965 disclose both porous films and absorbent layers for various sanitary articles.
The prior art does not disclose compositions for forming a highly wettable polyolefin, and particularly a highly wettable polypropylene. Substantially increased acceptance of polypropylene as a suitable nonwoven fabric for various incontinent products requires increased wettability of the polypropylene. Moreover, the polypropylene composition should be easily formed as a fiber which is spinnable, and ideally may be formed into a fabric sheet including nonwoven fibers.